The present invention relates to power tongs commonly used in drilling operations for threadably connecting and disconnecting tubular members. More particularly, the present invention relates to the hydraulic system for operating such a power tong in one of several speed/torque ranges, and to an open throat power tong with improved means for locking and unlocking the open throat tong door.
Power tongs may generally be classified as open throat or closed throat tongs. Closed throat tongs are described in U.S. Pat. Nos. 3,371,562, 3,483,774, 3,550,485, and 3,589,742. Since the rigid tong encompasses the pipe, the closed throat tong resists spreading and is generally capable of achieving high make up and break out torques. The disadvantage of a closed throat tongs, however, is that the tong body cannot be laterally put on or taken off a pipe. Open throat tongs, as shown in U.S. Pat. Nos. 3,021,739, 3,180,186, 3,196,717, and 4,084,453 enable the tong to move laterally with respect to the joint of pipe, and generally include a door latching mechanism for connecting the tong body in the open throat area. A variation of a closed throat tong is shown in U.S. Pat. No. 4,334,444, wherein both the tong body and the rotatable cam ring have pivotable portions for opening to laterally position the tong on the pipe, and both pivotable portions can be locked to approximate closed throat tong rigidity.
It is generally desirable that a power tong be operable at different speed/torque ranges and in both forward (make up) and reverse (break out) directions. Various systems have been devised for enabling a power tong to be operable at high speed/low torque while routinely threading together the joints of pipe, and low speed/high torque while making up the final desired pipe threading torque. U.S. Pat. No. 4,346,629 discloses a commonly used technique for manually shifting gearing of a tong to achieve either low speed or high speed output U.S. Pat. No. 3,635,105 discloses a tong with first and second motors for operating the ring gear, with a clutch driven part either idling along with the first motor or being driven by the second motor. U.S. Pat. No. 4,333,365 discloses a hydraulic system for operating a drive motor at different speed/torque ranges depending upon the activation of a pressure-intensifying or boosting means for selectively increasing the hydraulic fluid pressure to the motor. Finally, Canadian Patent No. 1,088,918 discloses a power tong employing a two-speed hydraulic motor.
The systems described in the above patents may allow both forward and reverse operation of a tong at different speed/torque ranges, but tong operators generally disfavor systems which require operation of a large number of controls. Thus, an operationally simplistic two speed tong may be preferred by an operator over a tong having a complicated drive system allowing for tong operation of various speeds by controlling numerous levers and gauges. Also, drive systems which utilize a mechanical gear shifting apparatus generally require slowdown of the tong prior to shifting, which increases the time required to make up pipe joints. Finally, many of the drive systems described in the above patents are mechanically and/or hydraulically complicated and expensive, and the advantages of a sophisticated tong hydraulic system generally cannot offset the disadvantages encountered if that tong experiences frequent breakdown in the field.
Most open throat tongs employ a door which preferably is both closed and latched (or locked in) before operating the tongs at high torque. Tongs may employ a door actuation mechanism to hydraulically close the tong door, as shown in U.S. Pat. No. 4,084,453. The problems encountered when a tong door is operated at high torque and the door is not properly latched are described in U.S. Pat. No. 4,170,907, which patent also describes a door interlock system for preventing a tong from operating if the door is not fully shut and secure. U.S. Pat. No. 4,334,444 also discloses a door interlock system, and further illustrates a hydraulic cylinder and latch for insuring complete closure of the door.
Tong operators nevertheless frequently do not utilize the door locking mechanism provided on a tong, because the locking of a tong door is another operation in a series of operations which must be rapidly and efficiently performed to make-up or break apart pipe. Also, it is common knowledge among tong operators that an open throat tong will not experience excessive spreading under low torque required in many operations. The door is thus often not closed for low torque operations provided the operators are cautious of the safety hazards associated with operating the tong when the door is open. Certain tongs may be provided a powered door closer, but powered door closing devices may also be a safety hazard to the operator standing in the area adjacent the door. If door interlock systems as described above are employed, operators may bypass the systems to allow more efficient tong operation. Also, the more sophisticated the system in the power tong, the higher the risk that the tong may breakdown in the field, and the more likely that the operator will develop techniques to avoid or bypass the system.
A further disadvantage of prior art tongs is that such tongs generally grip the pipe for rotation over a relatively limited contact area. As shown in U.S. Pat. No. 4,334,444, for instance, many tongs employ two pivotably movable or sliding heads with two elongate dies for each head. U.S. Pat. No. 4,346,629 discloses the usage of somewhat larger area dies in the heads, although these dies may not effectively grip the pipe for rotation without crushing or damaging the pipe.
The disadvantages of the prior art are overcome by the present invention, and improved methods and apparatus are described herein for making up and breaking apart joints of pipe.